1. Field of the Invention
The present invention relates to a wound treatment device with a bandage and heater that are essentially planar, yet flexible, and are connected or joined by an attachment device that promotes heat transfer from the heater through the bandage to a treatment area where the temperature of tissue is maintained by control of the heater's operation in a normothermic temperature range.
2. Description of the Related Art
The "normal" range of temperature for the human body is 37.degree. C..+-.1.degree. C. (36.degree. C.-38.degree. C.). This is termed the "normothermic" range. Humans exhibit a thermoregulatory response to core temperature changes as little as .+-.0.1.degree. C., wherein "core" as used herein refers to interior portions of the body. This extremely tight temperature control is necessary because virtually all cellular functions, chemical reactions and enzymatic reactions are optimum at normothermia.
Surface tissue varies in temperature according to where on the body it is located. The skin of the torso is usually hypothermic, while the skin of the legs is always hypothermic. The normal skin temperature of the distal leg is approximately 32.degree. C., which is considered to be "moderately hypothermic". The skin temperature of the distal leg of a patient with vascular insufficiency may be as low as 25.degree. C., which is "severely hypothermic". The hypothermic condition of wounds and ulcers inhibits healing. Severely hypothermic skin or wound tissue is in a state that may be termed "suspended animation". In suspended animation, tissue is living, but cellular functions necessary for cell division and collagen deposition are slowed or even stopped. Further, the immune system is inhibited,. The local application of heat to hypothermic skin will cause some degree of vasodilatation, resulting in an increase in local blood flow. Increased blood flow increases the subcutaneous oxygen tension (PsqO.sub.2) which, in turn, increases both collagen deposition and immune function.
Many references report that the immune system is inhibited by hypothermia and activated by mild hyperthermia (fever). Persp Biol Med:439-474, Spring 1980, reports that local body temperature is a critical factor determining host susceptibility, the location of lesions and contracting infectious diseases. New Eng J Med 305:808-814, 1981, reports that animals exposed to cold environments are more susceptible to infectious diseases, whereas exposure to high ambient temperatures often produces a beneficial result. Wound Rep Reg 2:48-56, 1994 and Acta Anaesth Scand 38:201-205, 1994, report that infections caused by a standard inoculum of e. coli or s. aureus were significantly more severe in hypothermic guinea pigs than in normothermic control animals. New Eng J Med 334:1209-1215, 1996, reports that hypothermic colorectal surgical patients had three times more wound infections (19% vs. 6%) than those who were kept normothermic during surgery with a Bair Hugger.RTM. patient warming system described in commonly assigned U. S. Pat. Nos. 5,324,320, 5,300,102 and 5,350,417. Further, six weeks of warming therapy with the Bair Hugger.RTM. patient warming system has successfully healed chronic progressive ulcers which heretofore have been resistant to antibiotic therapies.
As stated hereinabove, enzymatic reactions are promoted by normothemia. Both platelet adhesion and the clotting cascade result from a series of enzymatic chemical reactions. Research efforts have been reported that show hypothermic patients bleeding more than normothermic patients. J Thorac Cardiovasc Surg 104:108-116, 1992, and Ann Surg 205:175-181, 1987, report that skin cooling produces a reversible platelet dysfunction and prolonged bleeding times. Lancet 347 (8997):289-292, 1995, reports that mildly hypothermic total hip arthroplasty patients lost an average of 500 ml more blood and had an 88% higher incidence of transfusion than patients who were kept normothermic with the aforementioned Bair Hugger.RTM. Patient Warming System. Anesthesiology 85: A66, 1996, reports that hypothermic liver transplant patients required twice as many units of blood (18.6 vs. 9.8) and 57% more units of all blood products (46.2 vs. 29.4) than patients who were kept normothermic with the Bair Hugger.RTM. Patient Warming System.